An example of a valve having full-tank detecting means for a fuel tank is given in patent document 1. This valve has a first valve chamber connecting through to the inside of the fuel tank, and a second valve chamber connecting through to the first valve chamber and the outside, respectively, on top of this first valve chamber. In the first valve chamber, a first float is guided to be movable vertically so as to insert a guide projection into a guide hole formed on a valve chamber side wall. With this valve, the size of the first float can be made comparatively small in the vertical direction by such guide means, and the overall vertical size of the valve is made compact.
However, in this valve, when the fuel level reaches a height to let fuel into the first valve chamber, the first float ascends and closes the main connection channel with the second valve chamber, the fuel level inside the filler pipe is raised by a consequent increase, of pressure inside the tank, and an initial full-tank state is detected by a sensor in the fueling gun, but because the first float is guided by the aforementioned means, there are the following two problems:                (1) Because the clearance between the side face of the first float and the valve chamber side wall of the first valve chamber cannot be made large, both sides tend to contact each other due to running of the vehicle and produce a strange sound during descent of the first float.        (2) In the case when the first float becomes tilted, the first float may bite into the valve chamber side wall of the first valve chamber and become unmovable.        